Vision is an essential part of our well-being. Yet, the neural mechanisms allowing for the stable perception of visual objects under variations in their position are not sufficiently understood. In particular, we currently lack specific knowledge of how neural responses are transformed in the ventral visual pathway where visual object recognition is performed. Here we propose to probe neurons in visual areas V2 and V4 within the ventral pathway with natural stimuli in order to systematically determine their stimulus selectivity preferences. Natural stimuli offer a systematic way to study neural feature selectivity because they elicit robust responses from neurons at all stages of visual processing and because they constitute a stimulus set that is not tied to a particular hypothesis about prevalent neural feature selectivity. We have recently developed statistical methods that allow the characterization of the feature selectivity of neurons that are probed with natural stimuli, and which take into account nonlinear aspects of neural responses. Extending these methods to account for the fact that the responses of neurons in extrastriate visual areas can be tolerant to shifts in stimulus position (aim 1) will allow the systematic characterization of the stimulus preferences of these neurons under natural conditions. Responses of each neuron will be characterized according to the two localized stimulus features that are most relevant for the neural responses. This will provide a direct measure of the selectivity to curved elements in visual scenes thought to occur in V4 responses (aim 2). Finally, we will test whether specific parameters of neural feature selectivity, such as orientation and curvature, determines the directions of increased tolerance to shifts in object position (aim 3). Understanding the neural mechanisms of shape perception in the healthy nervous system is a key element in developing effective therapies for neurological disorders, such as apperceptive agnosia, where visual object recognition is impaired. PUBLIC HEALTH RELEVANCE: This study will elucidate the neural mechanisms responsible for shape perception. These neural processes are disrupted in several neurological disorders affecting vision. Understanding the neural mechanisms of shape perception in the healthy nervous system is a key element of developing effective therapies for neurological disorders where visual object recognition is impaired.